Equipment Grounding for Ungrounded System

[bobby ocampo]

It's a code violation if its not grounded! Nobody here is advocating avoiding grounding!

Your original post asks a clear question about equipment grounding, but you are now trying to prove the purpose of earth connection. These have different functions/purposes.

Equipment grounding is NOT ONLY BONDING included is connecting to earth. If the BONDED EGC isn't connected to earth it is very dangerous and may cause electric shock. Saying that the EARTH connection has no role in causing a reduction in electric shock is very dangerous.

 

[bobby ocampo]

That is still a minor player in preventing shock, especially under fault conditions.

Connection of the Bonded EGC to ground in my personal experience is not minor but a part of Equipment Grounding. If the EGC is not connected to Ground and is just connected to the neurtal and the neutral is not grounded it will be very dangerous. EGC should always be connected to the ground in a solidly grounded system.

The bonding is much more important, however even that does not remove the hazard.

In my humble opinion both are equally important in grounding.

If you have two pieces of equipment next to each other and one has a fault, there will a voltage between them, assuming that they each have their own EGC.

This is one of the reason why we are bonding. If both EGC are bonded there will be minimal voltage between them.

This voltage will be equal to the voltage drop on the EGC for the faulted equipment. The only way to remove that voltage is to clear the fault.
I have never said that the system should not be connect to earth, however that connection does very little to prevent shock, for a solidly grounded system, under fault conditions.

In my humble opinion connecting to earth of the BONDED EGC is as important as the bonding. I will develop an experiment to prove this and show you the result so you can also prove it to yourself. Our intention is not to have misconception for the safety of the people that are using electricity.

All of my comments are based on the much more common solidly grounded system. There is a big difference on what the connection to earth does for a single fault on a resistance grounded system. It does, for the most part, remove the hazardous voltage when a single fault occurs on those types of systems.

In transient or at the time the fault occurs based on the characteristics of electricity there will be a potential increase in voltage before it is reduced to zero during a short circuit fault. It will take time for the reactance of the transformer coil to discharge before the voltage becomes negligible.

 

[don_resqcapt19]

Connection of the Bonded EGC to ground in my personal experience is not minor but a part of Equipment Grounding. If the EGC is not connected to Ground and is just connected to the neurtal and the neutral is not grounded it will be very dangerous. EGC should always be connected to the ground in a solidly grounded system.

I never said that the connection to earth should not be made. I am saying it only plays a very small part in the safety of solidly grounded electrical systems under fault conditions.

This is one of the reason why we are bonding. If both EGC are bonded there will be minimal voltage between them.

There will be a potential between the faulted equipment and all of the other equipment that is connected to other EGCs that is equal to the voltage drop on the EGC between the fault and the main bonding jumper. This voltage will exist until the fault is cleared and can often exceed 40 volts on a 240 volt system with the EGC sized per 250.122. In addition everything connected to the other EGCs will have a potential to "remote" earth (earth outside the influence of a grounding electrode and often defined as 50' away from a grounding electrode) equal to the voltage drop on the system grounding conductor between the main bonding jumper and the system soure.

In my humble opinion connecting to earth of the BONDED EGC is as important as the bonding. I will develop an experiment to prove this and show you the result so you can also prove it to yourself. Our intention is not to have misconception for the safety of the people that are using electricity.

Yes, that is my intention also and the unless the grounding electrode will clear the fault it has very little effect on the safety of the system under fault conditions. One of the biggest misconceptions is the idea that the connection to earth makes our solidly grounded systems safe under fault conditions. It does not, unless you are standing on top of the grounding electrode.

 

[tryinghard]

Is equipment grounding important for ungrounded system?

What is the purpose of equipment grounding for ungrounded system?

Yes its extremely important, its purpose is to enable an effective ground-fault current path. To route shorts in such a way that enable the overcurrent protection device to operate, instantaneously if possible.

 

[tryinghard]

Equipment grounding is NOT ONLY BONDING included is connecting to earth. If the BONDED EGC isn't connected to earth it is very dangerous and may cause electric shock. Saying that the EARTH connection has no role in causing a reduction in electric shock is very dangerous.

The equipment grounding task really is simply bonding non current carrying items, additional to it is the earth connection and NEC requires this. Equipment grounding and bonding is done specifically to cause an effective ground-fault current path for the operation of OCP.

Grounding is done to ?limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials [non-current-carrying conductive materials].? 250.4(B)(1)

These are like shirts and pants, their both clothes but have different purposes.

If equipment grounding and bonding is correct a short will cause overcurrent protection to open in milliseconds, the earth connection plays no role in this function.

 

[bobby ocampo]

The equipment grounding task really is simply bonding non current carrying items, additional to it is the earth connection and NEC requires this. Equipment grounding and bonding is done specifically to cause an effective ground-fault current path for the operation of OCP.

Grounding is done to ?limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials [non-current-carrying conductive materials].? 250.4(B)(1)

Both are important otherwise if connecting to earth is not important the code should say so. Connecting to earth just like in UNGROUNDED SYSTEM AND HRG SYSTEM will limit the voltage to ground with connection to earth AND bonding EGC

If equipment grounding and bonding is correct a short will cause overcurrent protection to open in milliseconds, the earth connection plays no role in this function.

This is very dangerous in saying that connection to earth has no role for people protection. At t=0 in transient principle if EGC is not bonded then there will be a potential to ground in the energized metal enclosure.

This is very hazardous. If connection to earth will limit the potential to ground in High Resistance Grounded and UNGROUNDED SYSTEM, why will it not reduce the voltage to ground in a SOLIDLY GROUNDED SYSTEM. The coil of the transformer is not automatically de-energized at the instant of the single line to ground fault if it is not connected to earth. Inductance has a time constant up to how long will it reduce its voltage to minimum after shorting it. This is the reason why before maintaining a transformer all bushings are connected to the ground first to reduce the voltage to zero.

Hope nobody gets hurt or DIE by saying that connection to earth plays no role.

 

[winnie]

Mr. Ocampo,

Could you please restate the point you are trying to make or the question that you are asking? I have a very hard time figuring out if you are asking us something or telling us something.

Please also take the time to read the entirety of what people are writing, rather than just bits and snippits.

No-one says that you _shouldn't_ connect bonded metal to an earth electrode. But they have been trying to express the relative importance of that earth connection.

It is my opinion that the connection to the earth electrode has value; specifically in reducing the risk of high impedance high voltage sources (leakage from transformer primary to secondary, static charging, etc.) But for the vast majority of fault conditions, the connection to earth is of little importance.

The earth connection will _not_ significantly facilitate the operation of an OCPD. Only bonding back to the source will cause a short circuit that opens the OCPD.

The earth connection will significantly reduce the voltage between a fault point and the surrounding earth, but only if the fault point is near enough to the earth electrode. 'Near enough' depends upon the over-all system characteristics, but it is important to realize that a connection to earth at some _remote_ location (remote being further away than the 'sphere of influence' of the grounding electrode) is not necessarily a safety benefit where you happen to be standing. If the grounded and bonded metal in a structure becomes energized, then the soil near the grounding electrodes will be raised to the fault voltage...but soil just a few feet away will remain at its normal ground voltage.

In fact, depending upon circumstances, contact with metal bonded to a remote grounding electrode can present a safety hazard. Consider the example of a home electrical system, properly grounded with grounding electrodes, and properly bonded to the metal water piping. On the other side of the house from the service there is a hose spigot. The residents would experience shocks from that hose spigot to the soil next to the house; basically what they were feeling was the voltage difference between the two ground locations; the soil surrounding the grounding electrodes on one side of the house, and the soil where they were standing on the other side.

-Jon

 

[don_resqcapt19]

Both are important otherwise if connecting to earth is not important the code should say so. Connecting to earth just like in UNGROUNDED SYSTEM AND HRG SYSTEM will limit the voltage to ground with connection to earth AND bonding EGC

It just doesn't do a very good job of limiting the voltage to ground on a solidly grounded system, especially under fault conditions.

This is very hazardous. If connection to earth will limit the potential to ground in High Resistance Grounded and UNGROUNDED SYSTEM, why will it not reduce the voltage to ground in a SOLIDLY GROUNDED SYSTEM. The coil of the transformer is not automatically de-energized at the instant of the single line to ground fault if it is not connected to earth. Inductance has a time constant up to how long will it reduce its voltage to minimum after shorting it. This is the reason why before maintaining a transformer all bushings are connected to the ground first to reduce the voltage to zero.

The amount of current that is flowing when there is a ground fault in a solidly grounded system is much much greater than that of a HRG or LRG system. The current flow causes a votlage drop in the earth. As shown in the table in the green book, the voltage drop at 5' from the ground rod is ~85% of the voltage that is applied to the rod. The only way to eliminate the hazard for the solidly grounded system is to clear the fault.

Hope nobody gets hurt or DIE by saying that connection to earth plays no role.

I hope no one get hurt or dies because they think that the connection to earth will protect them.

 

[tryinghard]

...At t=0 in transient principle if EGC is not bonded then there will be a potential to ground in the energized metal enclosure.

If you are still talking about an ungrounded system it must have ground fault detection without this it will be in violation of 250.21. Ungrounded systems are not code compliant to allow a short to remain and especially to be undetected. Again an ungrounded system without ground fault detection completely circumvents the only reason for an ungrounded system!

If you are talking about a grounded system run a scenario: how long will your circuit stay energized with say .25 ohms on your effective ground fault path and a case frame short (any spec will do with ohms law)?

?If connection to earth will limit the potential to ground in High Resistance Grounded and UNGROUNDED SYSTEM

Exactly how will this happen at what distances? You will get great logical NEC guidance on this forum but now you're into the physics.

, why will it not reduce the voltage to ground in a SOLIDLY GROUNDED SYSTEM.

Because if you installed a code compliant circuit, or feeder, the OCP has opened in seconds or even milliseconds, the circuit will be off.

The coil of the transformer is not automatically de-energized at the instant of the single line to ground fault if it is not connected to earth...

On a grounded system it most certainly should be if you have installed an effective ground fault path!

Fault current is only trying to return to source, one short on an ungrounded system has no potential it?s like a bird on a wire. The earth grounding is still required and there will be zero use of electricity with a short. There is no potential to earth because none of the transformers are bonded.

Fault current is not trying to go to earth if it is the circuit is in violation of NEC.

If a fault happens I=E/R proves the need for an intentional equipment ground fault path to enable the operation of overcurrent protection.

 

[iwire]

If you are still talking about an ungrounded system it must have ground fault detection without this it will be in violation of 250.21. Ungrounded systems are not code compliant to allow a short to remain and especially to be undetected. Again an ungrounded system without ground fault detection completely circumvents the only reason for an ungrounded system!

You lost me there, the NEC does not require all ungrounded systems to have ground fault indicators.

See this post #41

 

[tryinghard]

You lost me there, the NEC does not require all ungrounded systems to have ground fault indicators.

See this post #41

So how does 250.20(B) override/integrate with 250.21?

 

[iwire]

So how does 250.20(B) override/integrate with 250.21?

In 250.20(B) we are told what systems are required to be grounded.

If a system does not have to be grounded by 250.20(B) you can chose not to ground it and you do not have to provide fault indicator.

480 Delta is an example of a system that is not required by 250.20(B) to be grounded.

Then you get to 250.21 list specific times you can ignore 250.20(B) but if you do that then you need ground fault indicators.

The NEC requirement for ground fault indicators I believe is not that old.

Obviously it seems prudent to provide fault indicators bit it is not always required.

 

[weressl]

In 250.20(B) we are told what systems are required to be grounded.

If a system does not have to be grounded by 250.20(B) you can chose not to ground it and you do not have to provide fault indicator.

480 Delta is an example of a system that is not required by 250.20(B) to be grounded.

Then you get to 250.21 list specific times you can ignore 250.20(B) but if you do that then you need ground fault indicators.

The NEC requirement for ground fault indicators I believe is not that old.

Obviously it seems prudent to provide fault indicators bit it is not always required.

(B) Ground Detectors.​

​

​

Ungrounded alternating current
systems as permitted in 250.21(A)(1) through (A)(4) operating
at not less than 120 volts and not exceeding 1000
volts shall have ground detectors installed on the system.

.......​

A (4) Other systems that are not required to be grounded in
accordance with the requirements of 250.20(B)

It seems to me that​

• all systems listed under 250.21 AND​
• not specifically excepted under 250.20(B)​
• ARE the ones allowed to be installed without grounding AND​
• opperate between 120V and 1000V​

shall have ground detectors.​

 

[iwire]

It seems to me that

I am not seeing it, not saying your not right, just not seeing it.

Can you try it another way.

I only see ground fault indicators required for 250.21(1) through (4).

 

[weressl]

I am not seeing it, not saying your not right, just not seeing it.

Can you try it another way.

I only see ground fault indicators required for 250.21(1) through (4).

Bob,

...and A(4) says all systems that are not specifically listed in 250.20(B).

That is why I reprinted 250.20(B)

 

[iwire]

Bob,

...and A(4) says all systems that are not specifically listed in 250.20(B).

Ah got it now, sometimes you just gotta whack me over the head to see things, Thanks. :smile:

 

[bobby ocampo]

It just doesn't do a very good job of limiting the voltage to ground on a solidly grounded system, especially under fault conditions.

I would still believe that both are equally important. Clearing of fault flowing through a low impedance path through the bonded EGC and connection to earth to reduce voltage to ground. Not one but BOTH are equally important.

The amount of current that is flowing when there is a ground fault in a solidly grounded system is much much greater than that of a HRG or LRG system. The current flow causes a votlage drop in the earth. As shown in the table in the green book, the voltage drop at 5' from the ground rod is ~85% of the voltage that is applied to the rod. The only way to eliminate the hazard for the solidly grounded system is to clear the fault.

Both are IMPORTANT. this is the reason why many ground rod are installed in a substation to reduce the step potential and are interconnected or bonded together so that during a fault a personnel will not receive a shock with step potential. Both bonding and connection to ground are important. A big part of the design is the measurement of the grounding resistance to deterimine the number of ground rods and the connection of the mesh in a substation.

I hope no one get hurt or dies because they think that the connection to earth will protect them.

My humble opinion is BOTH are of equal importance. Never have i commented that EGC is not important. Saying the connection to earth is of no value is hazardous. For safety in the use of electricity BOTH bonded EGC and connection to earth should be done and not only one of the above.

 

[weressl]

I would still believe that both are equally important. Clearing of fault flowing through a low impedance path through the bonded EGC and connection to earth to reduce voltage to ground. Not one but BOTH are equally important.




Both are IMPORTANT. this is the reason why many ground rod are installed in a substation to reduce the step potential and are interconnected or bonded together so that during a fault a personnel will not receive a shock with step potential. Both bonding and connection to ground are important. A big part of the design is the measurement of the grounding resistance to deterimine the number of ground rods and the connection of the mesh in a substation.



My humble opinion is BOTH are of equal importance. Never have i commented that EGC is not important. Saying the connection to earth is of no value is hazardous. For safety in the use of electricity BOTH bonded EGC and connection to earth should be done and not only one of the above.

Unfortunately you are talking to a body of people - many are excluded - who are 'trained' by cute colored drawings developed by people without science background. No checks or balances or peer reviews are required, nor scientific explanation is offered. Understanding The Mythical ground connection remains ever elusive, so don't bother pushing it.:wink:

 

[iwire]

Both are IMPORTANT. this is the reason why many ground rod are installed in a substation to reduce the step potential and are interconnected or bonded together so that during a fault a personnel will not receive a shock with step potential. Both bonding and connection to ground are important. A big part of the design is the measurement of the grounding resistance to deterimine the number of ground rods and the connection of the mesh in a substation.

There is a large difference between the majority of electric work being done and substations.

At the voltages we usually deal with (under 277 volts or 120 volts to ground the connection to earth does virtually nothing.

Raise the voltage to 10, 20, 30 KV and that connection to earth becomes much more effective.

Also if I recall substations have entire grounding grids under them for step potential protection. With an entire grid under foot your essentially 'standing on the rod' as Don mentioned earlier.

 

[bobby ocampo]

Mr. Ocampo,

Could you please restate the point you are trying to make or the question that you are asking? I have a very hard time figuring out if you are asking us something or telling us something.

Please also take the time to read the entirety of what people are writing, rather than just bits and snippits.

Dear Mr Winnie,
I try my best to answer point by point of the comments and not just bits and snippits.

No-one says that you _shouldn't_ connect bonded metal to an earth electrode. But they have been trying to express the relative importance of that earth connection.

Dear Mr. Winnie,
There should be no relative importance. It is hazardous to say that connection to earth has of little importance. This is subject to mis-interpretation. Both should be important in the protection of personnel against the hazards arising in the use of electricity.

It is my opinion that the connection to the earth electrode has value; specifically in reducing the risk of high impedance high voltage sources (leakage from transformer primary to secondary, static charging, etc.)

This include ground fault inside the transformer. I agree that connection to earth has value even in an internal short circuit fault such as a single line to ground fault in the windings of the transformer.

But for the vast majority of fault conditions, the connection to earth is of little importance.

Both are important and having a RELATIVE importance is subject to misinterpretation and is hazardous. BOTH should be important.

The earth connection will _not_ significantly facilitate the operation of an OCPD. Only bonding back to the source will cause a short circuit that opens the OCPD.

Never did I say that connection to earth will facilitate operation of OCPD. Connection to earth is reducing potential of accidentally energized metal part to reference ground potential.

The earth connection will significantly reduce the voltage between a fault point and the surrounding earth, but only if the fault point is near enough to the earth electrode.

I respectfully agree. This is the reason why several grounding rods are installed in a substation depending upon the measured resistance of the earth. This ground rods are interconnected and bonded together to reduce step potential during different types of short circuit fault including the most common line-to-ground fault.

'Near enough' depends upon the over-all system characteristics, but it is important to realize that a connection to earth at some _remote_ location (remote being further away than the 'sphere of influence' of the grounding electrode) is not necessarily a safety benefit where you happen to be standing. If the grounded and bonded metal in a structure becomes energized, then the soil near the grounding electrodes will be raised to the fault voltage...but soil just a few feet away will remain at its normal ground voltage.

BOTH should be important. Both bonded EGC and connection to earth. Both are important.

In fact, depending upon circumstances, contact with metal bonded to a remote grounding electrode can present a safety hazard. Consider the example of a home electrical system, properly grounded with grounding electrodes, and properly bonded to the metal water piping. On the other side of the house from the service there is a hose spigot. The residents would experience shocks from that hose spigot to the soil next to the house; basically what they were feeling was the voltage difference between the two ground locations; the soil surrounding the grounding electrodes on one side of the house, and the soil where they were standing on the other side.

-Jon

BOTH should be important. Both bonded EGC and connection to earth. Both are important.